Portable electronic devices such as audio players or digital cameras of the portable type conventionally have incorporated therein a dry cell or secondary cell serving as the power source to realize the portability of the device. In some cases, however, it is desired to connect a commercial a.c. power source or like external power source to such a device and operate the device therewith. This nevertheless entails the problem that the provision of a connector for connecting the external power source to the portable electronic device renders the device greater in size.
In recent years, USB has attracted attention as a universal interface for connecting a plurality of peripheral devices in common to a host personal computer, and studies are underway for providing USB connectors, which are compliant with the USB standard, on various portable electronic devices. The USB connector has a pair of data terminals D+ and D−, power source terminal and ground terminal, and can be used for supplying power to peripheral devices by way of the power source terminal.
Accordingly, it appears feasible to provide the USB connector on a portable electronic device for use with an a.c. adaptor (external power source) connectable to the power source terminal of the USB connector, and to connect the a.c. adaptor to the power source terminal of the USB connector for the supply of power to the device, the USB connector thus serving also as a connector for the connection of the external power source, whereby an increase in the size of the electronic device is avoidable.
However, it is usual practice with the portable electronic device (compliant with the USB standard) having the USB connector to provide a main CPU for executing predetermined device operation processing for various operations of the device including reproduction of data, and a USB controller separate from the main CPU and adapted to execute predetermined data processing for carrying out data communication with the personal computer through the USB connector so as to ensure simplified processing. When the personal computer is connected to the USB connector on the portable electronic device in this case, it is necessary for the USB controller to conduct data communication with the personal computer with a definite period as required by the USB standard, so that the leadership in data processing is taken over by the USB controller from the main CPU. This entails the problem that even if the user gives the portable electronic device a command for data reproduction (play operation), the main CPU is unable to rapidly execute device operation processing for data reproduction.
Further while the USB controller is connected to the personal computer for data communication, some kind of data is handled also between the main CPU and the USB controller. This gives rise to the problem that the main CPU must execute very complicated processing since there is a need for the main CPU to execute device processing for data reproduction in this state.